In a nonvolatile memory, it is becoming difficult to scale down a floating gate (FG) type flash memory or a metal/oxide/nitride/oxide/silicon (MONOS) type flash memory. Therefore, scaling-down using an operation principle different from these memories has been continuously looked for. Nonvolatile memories having various structures, such as a ferroelectric random access memory (FeRAM), a resistive random access memory (ReRAM), a phase change random access memory (PCRAM), a magnetic random access memory (MRAM), or a three-dimensional memory have been examined.
Among these memories, the FeRAM using a ferroelectric substance had the following problems. That is, the FeRAM included a material difficult to handle, such as lead, and reduction in thickness of the FeRAM was difficult due to a size effect. Therefore, it was difficult to put the FeRAM into practical use except the FeRAM for a limited purpose, such as radio frequency identification (RFID) cards including a small-scale FeRAM for low power consumption.
In such a deadlock, a hafnium oxide film has been reported as a ferroelectric film not containing lead, not difficult to make a thin film thereof, capable of low voltage operation, that is, low power consumption operation, and capable of holding a record for a long time. It is expected to realize the ferroelectric memories, such as FeRAM having a large capacity by using this hafnium oxide film.